Contact system for interfacing a semiconductor wafer to an electrical tester

ABSTRACT

Disclosed herein are exemplary embodiments of a contact system (referred to as a “Z-block”) for interfacing a semiconductor wafer to an electrical tester, and methods for making the same. In a preferred embodiment, the Z-block comprises three stacked pieces or layers: an upper and lower piece which are similar in structure, and a unique middle piece. The pieces each contain corresponding locking holes and probe pin holes. The locking holes are strategically arranged on each of the pieces to allow the stacked piece structure to be locked together at various points during its manufacture. After alignment of the probe pin holes in the various pieces, probe pins are injected into these holes. The probe pins are then aligned and locked into place by moving the middle piece relative to the upper and lower pieces. Such locking of the probe pins is accomplished through interaction of the middle piece with the shape of the probe pins, which prevents the probe pins from slipping out of the probe pin holes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. application Ser. No.10/819,673, filed Apr. 7, 2004, now U.S. Pat No. 7,176,702, which isincorporated herein by reference in its entirety and to which priorityis claimed.

FIELD OF THE INVENTION

This invention relates a contact system for testing semiconductordevices, and preferably to a contact system for interfacing asemiconductor wafer to an electrical tester.

BACKGROUND

As is known, semiconductor integrated circuit devices (“chips”) can betested while they are still present on the semiconductor wafer on whichthey were formed. Such wafer level testing is traditionally accomplishedon a per chip basis, in which probe tips are brought into contact withbond pads for a given chip, the chip is stimulated and tested throughthe probe tips via a tester, and then the wafer is indexed and moved tothe next chip which is similarly tested, etc.

However, systems also exist which are capable of testing an entiresemiconductor wafer, i.e., all chips on the wafer simultaneously andwithout the need to index from chip to chip. While such systems can beused to test the chips on the wafer for basic functionality, they arealso particularly useful to stress the chips for a limited period oftime for the purpose of weeding out early latent failures, what is knownin the art as “burn in.” When burning in a wafer, and as shown in FIG.1A, signals are sent from a tester 10 through a cable conduit 12 andedge connector 14 to a burn in board or “fan out” board 20. As oneskilled in the art will appreciate, the burn in board 20, whichtypically constitutes a Printed Circuit Board (PCB), contains contactpoints 22 on its underside (shown in phantom) which match the locationsof the bond pads 42 on the wafer 40 being tested or burned in. (Onlyseveral corresponding contact point 22/bond pad 42 pairs are shown inFIG. 1A for simplicity, although one skilled in the art will recognizethat tens of thousands or more can be present). Such bond pads 42 mayconstitute redistribution bond pads routed to convenient locations andat a more relaxed pitch that is easier to probe than are traditionalbond pads.

To electrically and physically mate the contact points 22 with the bondpads 42, an intermediary structure is interposed therebetween. Thisintermediary structure is sometimes known as a “Z-block,” which is sonamed because it mates the contact point 22/bond pad 42 pairs along theZ (or vertical) axis. The Z-block 30 contains holes 45 therethroughwhich similarly match the location of each contact point 22/bond pad 42pair. Interposed in each hole is a conductive probe pin 32. When theburn in board 20, the Z-block 30, and the wafer 40 are sandwichedtogether during a testing or burn-in operation, and as shown incross-section in FIG. 1B, the ends of the probe pins 32 will contact thecontact points 22 on one side of the Z-block 30 and the bond pads 42 onthe wafer 40 on the other side. Because of the mechanical nature of thecoupling of this stack, it is preferred that the probe pins 32 bedeformable in a spring like manner. Many shapes are possible for theprobe pins 32, which may comprise helical spring, leaf springs, “pogopins,” springs made from flat sheets of metal, etc.; the S-shaped probepin shown in the Figures is merely exemplary, and other probe pindesigns will be discussed in this disclosure.

It can be difficult to construct a Z-block 30, as a number of parametersconstrain its design. For example, the Z-block must capture the probepins 32 so that the pins will not fall through the Z-block. This usuallyrequires the use of a probe pin 32 having two effective diameters: anend diameter D1 and a body diameter D2, as shown in FIG. 2A. In thisexample, the probe pin 32 is essentially a helical spring with straightends used to contact the contact points 22/bond pads 42, although otherpin shapes are possible. To accommodate and capture such a probe pin 32,the Z-block 30 must in turn also contain through holes 45 with twodifferent diameters: one diameter D3 sufficiently large for theeffective diameter of the probe pin end (D1) to fit through, but smallerthan the effective diameter of the probe pin body diameter (D2); and asecond diameter D4 sufficiently large to accompany the probe pin bodydiameter (D2).

This relationship can be accomplished in different ways. For example,and as shown in FIG. 2A, the Z-block 30 can be formed of two separatepieces 50 a and b. Each piece has holes 45 drilled therein correspondingto the eventual location of the probe pins 32. Through the use of anangled drill bit, holes 45 having a conical ends can be formed whichmeet the two-diameter requirement noted above for retaining the pins 32.Such holes 45 must be drilled precisely along the Z-axis lest thediameters of the holes (e.g., D3) become skewed or non-uniform, whichcan be very difficult or expensive to accomplish. Ultimately, the probepins 32 are placed within the holes 45 in the lower of the two pieces 50a, and thereafter the upper piece 50 b is affixed (e.g., bolted, glued,etc.) to the lower piece 50 a to capture the probe pins 32, as shown inFIG. 2B. FIGS. 2C and 2D disclose other Z-block geometries for capturingthe probe pins 32 which again use multiple affixable pieces, although inthese examples the pieces are drilled with perfectly cylindrical holes45.

Regardless of the scheme used to form the Z-block 32, ultimately all ofthe schemes involve the same step of (1) placing the pins 32 into holes45 in at least one lower piece of the Z-block, and (2) placing at leastone other piece of the Z-block over the pins to capture them andaffixing the pieces together. But this is difficult to do in practice.The probe pins 32 are very delicate, being on the order of 100 mils inlength and made of wire which may have a thickness of approximately 3mils for a 100 mil length coil spring pin. It is therefore difficult toinsert the probe pins 32 into the lower piece 50 b such that their endsprotrude through the smaller diameter holes (D3). Moreover, if the probepins 32 lay askew in their holes 45 when the upper piece 50 b is placedon top of the lower piece 50 a, the ends of the pins 32 may not passthrough the holes 45 in the upper piece, and instead will become bentwithin the holes and unable to make contact with the points/pads 22 or42. This problem is exacerbated when it is recognized that a typicalZ-block 30 may contain tens of thousands of probe pins 32, thusrequiring the ends of the pins to simultaneously pass through the upperpiece 50 b when it is mounted to the lower piece 50 a, a formidablechallenge. Damage to any one of these pins 32 may require opening andre-working the Z-block 30 to replace affected or damages pins, whichrequires unaffixing (e.g., unbolting) the upper and lower pieces 50 aand 50 b. This reopening procedure too can cause problems, as thisoperation can tend to drag the otherwise properly-aligned pins 32 out oftheir holes 45, which can occur if the delicate pins bind to the smallerdiameter portions (D3) of the holes. This can be a problem even if nopins 32 are damaged through assembly of the Z-block, but instead becomeworn though use and need replacement.

Moreover, capturing the spring limits the sorts of probe pins that canbe used with known prior art Z-block approaches. As noted above, theprobe pins 32, be they springs, pogo pins, etc., necessarily mustcontain end portions with smaller effective diameters (D1) than the mainbody portion of the pins (D2) so that they can be captured, but stillprotrude from, the holes 45 (D3, D4). Such a limitation to the design ofthe probe tips is unfortunate. For example, consider the probe pin 32 ofFIG. 3, which has a flat, long end 32 a. This end design for the pin maybe used, for example, as the portion of the pin 32 to make contact withthe bond pads 42, which is beneficial as a flat end 32 a is less likelyto stab and damage the bond pads 42. However, such a pin design cannotbe used with prior art means for capturing the springs as shown in FIGS.2A-2D, because the effective diameter of end 32 a (D5) is greater thanthe effective diameter of the body of the spring (D6).

Another problem that prior art Z-block designs do not adequately addressis the issue of probe pin orientation within the holes of the Z-block.As shown by the probe pin design of FIG. 3, not all probe pins arerotatably symmetrical about their long axis 60. But probe pins 32, whenplaced in the holes 45 in prior art Z-blocks, will be able to rotatefreely within the holes 45. This is undesirable, especially forasymmetric probe pins. For example, as shown in FIG. 4, if the probe pinof FIG. 3 was mounted within a prior art Z-block, it would be allowed toturn such that the various ends 32 a of the probe pins 32 would becomemisaligned (in solid lines). Such non-uniformity is undesirable as itmay make contact of such ends to bond pads 42/contact points 22unreliable or could result in shorting and limiting probe design. Itwould therefore be preferable for the probe pins 32 to be non-movablyaligned in the holes, which would, for example, allow the ends 32 a tohave a uniform orientation (in dashed lines).

In short, there is room to improve to Z-block designs. Such improvementwould preferably make assembly of the Z-block easier, installing andservicing of the probe pins easier, would accommodate a wide variety ofprobe pin designs, and would be cheaper to manufacture. This disclosurepresents such solutions.

SUMMARY OF THE INVENTION

Disclosed herein are exemplary embodiments of a contact system (referredto as a “Z-block”) for interfacing a semiconductor wafer to anelectrical tester, and methods for making the same. In a preferredembodiment, the Z-block comprises three stacked pieces or layers: anupper and lower piece which are similar in structure, and a uniquemiddle piece. The pieces each contain corresponding locking holes andprobe pin holes. The locking holes are strategically arranged on each ofthe pieces to allow the stacked piece structure to be locked together atvarious points during its manufacture. After alignment of the probe pinholes in the various pieces, probe pins are injected into these holes.The probe pins are then aligned and locked into place by moving themiddle piece relative to the upper and lower pieces. Such locking of theprobe pins is accomplished through interaction of the middle piece withthe shape of the probe pins, which prevents the probe pins from slippingout of the probe pin holes.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the inventive aspects of this disclosure will be bestunderstood with reference to the following detailed description, whenread in conjunction with the accompanying drawings, in which:

FIGS. 1A and 1B show the basic components of a prior art system fortesting or burning in a wafer using an intermediary Z-block between theburn in board and the wafer.

FIGS. 2A-2D shows prior art Z-block approaches in cross section, andshows capture of the probe pins within pieces of the Z-block.

FIG. 3 shows a spring design which can be used with the disclosedZ-block design, but which is not suitable for use with the Z-blockdesigns of FIGS. 2A-2D.

FIG. 4 shows rotational misalignment of the probe pins of FIG. 3.

FIGS. 5A-5B show the various locking holes (b, c, d) and probe pinsholes (a) in the upper, middle, and lower portions of an embodiment ofthe disclosed Z-block, and the relative orientation of those holes.

FIGS. 6-15 show sequential steps in assembling a Z-block using thepieces of FIGS. 5A-5B, including initial locking of the stack, alignmentof probe pin holes and temporary locking of the same, insertion of theprobe pins, alignment of the probe pins, and locking of the probe pinsin their holes.

FIGS. 16A-16D show alternative designs for the probe pins and the piecesusable in the context of the disclosed Z-block.

FIG. 17 shows an alternative probe pin locking scheme.

FIGS. 18A-18C show alternative Z-block designs using two, four, and fivepieces.

DETAILED DESCRIPTION

Disclosed herein is an improved Z-block design, and methods for itsmanufacture. The disclosed design is simple to manufacture, easy toinstall the probe pins into, easy to service, and can accommodate anumber of probe pin designs. Moreover, the design allows for rotation ofthe probe pins within the Z-block so that they can be aligned, andlocking of those aligned pins into place.

FIGS. 5A and 5B illustrate a simple illustrative embodiment of theZ-block 100's design, and illustrate the various pieces of the Z-blockin a plan view and perspective view respectively. In this embodiment,the Z-block 100 comprises three different pieces (e.g., plates): anupper piece 110, a middle piece 120, and a lower piece 130. When theZ-block is assembled, each of these pieces is stacked and lockedtogether to capture the probe pins 150, as will be seen in subsequentdrawings.

Each of the pieces 110, 120, 130 contains a number of holes (a, b, c, d)which perform various functions in the Z-block. Holes 110 a, 120 a, 130a are the holes that ultimately will contain the probe pins 150; only afew representative holes are shown in FIGS. 5A and 5B for clarity, buttens of thousand can be present. The b, c, and d holes allow the piecesof the Z-block 100 to be locked together at various points during theZ-block's assembly, or upon final assembly of the Z-block. Specifically,holes 110 b, 120 b, 130 b allow the Z-block to be locked prior to probepin insertion; holes 110 c, 120 c, 130 c allow the Z-block to be lockedduring pin insertion; and holes 110 d, 120 d, 130 d, allow the Z-blockto be locked after probe pin insertion and capture, which completesassembly of the Z-block. These various locking procedures will bedescribed in further detail in conjunction with FIGS. 6-15.

Although the locking holes (b, c, d) are preferably disposed around theperiphery of the pieces 110, 120, 130 and away from the working area ofthe pieces where the probe pins are located, this is not strictlynecessary. Moreover, although only four of each of these locking holesare shown, more or less may be present (three, six, etc.).

The various holes (a, b, c, d) are preferably the same in the upper andlower pieces 110 and 130, and in this regard the same piece can be usedfor both. Holes 110 a, 130 a, which ultimately hold the springs, have adiameter of approximately 15 mils, while holes 110 b-d, 130 b-d have alarger diameter of roughly 1 mm. Of course, other diameters can be used.The middle piece 120, however, is different; its probe pin holes 120 aare the same as that of the upper and lower pieces 110, 130, as are itslocking holes 120 c. However, locking holes 120 b are larger in diameterthan corresponding holes 110 b, 130 b, measuring approximately 2 mm indiameter. Furthermore, locking holes 120 d are linearly shifted withrespect to corresponding holes 110 d, 130 d, although they are equal insize (again, approximately 1 mm). (They may also be shifted is otherways, such an angularly along a common radius as shown in FIG. 17).These differences in the location and sizes of the various holes betweenthe middle piece 120 and the upper/lower pieces 110, 130 are illustratedin FIG. 5A, in which corresponding holes for the upper/lower pieces areshown in dotted lines on the top view of the middle piece 120. Ofcourse, the sizes of the holes are greatly exaggerated to illustratetheir differences and functions more clearly.

The pieces 110, 120, and 130 of the Z-block 100 are preferably formedfrom Printed Circuit Board (PCB) materials, such as Arlon 55 NT or FR4,although other materials can be used as well. It is preferred to useinsulating materials for the pieces (or materials that have been coatedor treated to make then insulating) so that the probe pins 150 in theZ-block 100 will not short to each other. As the Z-block 100 may be usedin high-temperature applications, such as during bum in, it is alsopreferred that materials with relatively low Coefficients of ThermalExpansion (CTEs) be used which have a similar CTE to the wafer beingtested. If necessary, non-functional holes can be drilled in the piecesto reduce their bulk to effectively lower their CTEs and allow forconstrainment. The pieces 110, 120, and 130 can also be coated to reducesliding friction and to prevent them from bonding or sticking together.(As will be seen herein, the ability to slide the pieces with respect toone other is an important aspect of some embodiments of the invention).Teflon or Parylene works well for such coatings.

As will be seen later, the thicknesses for the pieces 110, 120, 130 canvary depending on the probe pin design that is to be used with theZ-block 100. However, in a preferred embodiment, the upper and lowerpieces 110, 130 are approximately 60-70 mils thick, while the middlepiece 120 is approximately 15-20 mils thick. While it is illustratedthat the pieces 110, 120, 130 forming the Z-block 100 are circular (tomatch the wafer 40 with which it interfaces), the pieces may take onother shapes, such as a rectangular or square shapes, as shown in dottedlines.

Referring now to FIG. 6, a cross-sectional view of the beginning of theassembly of the Z-block 100 is illustrated. In this illustration, eachof the locking holes (b, c, d) are shown so that their various functionscan be better understood. However, as FIGS. 5A and 5B reveal, such holesneed not necessarily occur along a given cross section. Also, forconvenience, the diameter of the probe pin holes (“a”) are shown asbeing of the same diameter as some of the locking holes, although inreality they would be different, and typically smaller.

FIG. 6 shows the three pieces 110, 120, 130 mounted on an assembly plate155 and spaced therefrom by spacers 157. The spacers 157 areapproximately 15 mils thick and as will be made clear later provide forclearance of the ends of the probe pins once they are inserted into thepieces. The assembly plate 155 is preferably formed of a smooth materialwhich will not bind to the probe pins, such as Pyrex, but can compriseany number of materials. The entire assembly is preferably mounted undera low-resolution optical microscope to 158 allow an operators to moreeasily perform the various assembly steps discussed herein.

As initially shown in FIG. 6, the three pieces 110, 120, 130 are roughlyaligned with one another to form a stack. However, to prepare foreventual insertion of the probe pins, the stack is preferably stabilizedusing locking pins or dowels 170, as shown in FIG. 7. The dowels 170 arepreferably stainless steel and 1 mm in diameter, and are placed in the“b” locking holes in the various pieces. Holes 110 b, 130 b are slightlyundersized (approximately 0.97 mm) to allow for a snug fit when thedowels 170 are pressed into the “b” holes by an operator, which canoccur by hand or by using a tool (e.g., tweezers). Once the dowels 170are in place, the stack is basically mechanically stable. Dowels 170 arepreferably of approximately the same thickness as the stacked pieces,but can also protrude from the top or bottom of the stack so long asthey will not affect performance of the Z-block 100 in operation. Dowels170 could also extend from both sides for the purpose of keying to PCBtest structures and/or assembly structures, etc.

At this point, the upper 110 and lower 130 pieces of the Z-block arerigidly affixed to one another, but the middle piece 120 is slidablebetween the two by virtue of its larger hole 120 b. As this hole ispreferably 2 mm in diameter, the middle piece 120 can be shiftedapproximately +/−0.5 mm with respect to the dowel 170 in the X or Y(i.e., horizontal) direction. For example, as shown in FIG. 8, themiddle piece 120 has been shifted approximately 0.5 mm to the right.Because middle piece 120 is moveable, an operator can push or pull themiddle piece 120 to align the probe pin holes 110 a, 120 a, 130 a toallow for smooth insertion of the probe pins 150. This is facilitated bymaking the middle piece 120 slightly larger in size (e.g., diameter)than the upper/lower pieces 110, 130 so that the edges of the piece 120can be grasped by the operator. (This size difference is not shown inthe Figures for clarity). To align the middle piece 120, the operatorlooks through the microscope 158 at a certain sample of probe pins holes(“a”) across the working surface to ensure that perfect, non-eclipsedcircles can be seen within the holes. A light mounted on the undersideof the Pyrex assembly plate 155 (not shown) can facilitate thisprocedure. Optionally, alignment of the middle piece 120 can beautomated, using a motorized X-Y stage and optical alignment routinessimilar to those traditionally used for wafer probing. Alignment canalso be accomplished, or can be more easily implemented, by pushingdowels with tapered tips into the probe pin holes (“a”), or into otherlocking holes (not shown) having a diameter just under those of theprobe pin holes (“a”).

Once the middle piece 120 has been aligned, the stack is mechanicallyfixed to lock the middle piece 120 into place so that it can longer behorizontally shifted. This is accomplished by placing a second set ofdowels 180 into the “c” holes within the pieces 110, 120, 130, as shownin FIG. 9. Dowel 180 is again preferably stainless steel and 1 mm indiameter. However, dowels 180 are substantially longer than dowels 170and protrude from the top of the stack (perhaps 0.25 to 0.5-inch), whichfacilitates their eventual removal. In this regard, note that the “c”holes are all uniform in diameter and are drilled such that theiralignment correspond to alignment of the probe pin holes (“a”). Thus,once the probe pin holes “a” have been manually aligned, the “c” holesare aligned also. The “c” holes are preferably slightly larger (e.g.,1.03 mm) than the dowel 180 to allow it to be easily inserted andretrieved. As a result, dowel 180 can come to rest on the surface of theassembly plate 155.

Once alignment of the middle piece 120 has been accomplished and hasbeen locked into place using dowels 180, the probe pins 150 can beinserted into the probe pin holes (“a”) as shown in FIG. 10. The probepins 150 can be inserted in any number of ways, such as by hand, throughthe use of a pneumatic “gun” to “shoot” the pins into the holes, etc. Inthe example shown, the probe pins 150 of FIG. 3 are used, but of coursemany other type of probe pins designs (helical, leaf springs, etc.) canbe used.

Two points are worthy of note at this stage. First, because the probepin holes (“a”) have been aligned, the probe pins 150 are easilyinserted into the Z-block 100. This is much easier when compared to theprior art approaches discussed above in which the pins are first placedinto non-uniform diameter holes and later sandwiched between two piecesof the Z-block. As a result of the disclosed approach, the probe pins150 are much less susceptible to damage or binding during Z-blockassembly. Second, notice that one of the probe pins 150 (second from theleft) is rotationally misaligned with respect to the other pins.Specifically, this pin is rotated at 90-degrees with respect to theother pins, as best shown in the top view of the stack in FIG. 11. Thisis important to note now, because in subsequent steps this rotationalmisalignment within the holes will be fixed, thus illustrating anotherimportant advantage to the disclosed approach.

Once the probe pins 150 are in place, the dowels 180 can be removed asshown in FIG. 12, which re-exposes the “c” holes. This once again allowsthe middle piece 120 to move relative to the upper/lower pieces 110,130.

As will be seen later, one aspect of the disclosed invention is abilityto move the middle piece 120 to lock the probe pins into place. However,prior to this step in the assembly process, it may be desirable torotationally align the pins in the probe pins holes (“a”). This isespecially desirable if the pins are not rotationally symmetrical abouttheir long axis, or if for some reason the probe pins have special endsthat are advantageously oriented in a predictable format. Moreover,rotational alignment ensures that the probe pins can be subsequentlylocked without damage. Rotational alignment can also be critical forachieving consistent probe tip pointing accuracy necessary tointerfacing with small pads or contacts, such as traditional wafer bondpads.

Such alignment of the probe pins can be affected by moving the middlepiece 120. In a preferred embodiment, and referring to FIGS. 13A and13B, the middle piece 120 is moved along a path 190. Several routes forpath 190 are possible to perform the alignment function, but in apreferred embodiment, the path 190 first contemplates moving the middlepiece 120 to a position that ideally would lock the probe pins 150 intoplace, which in the illustrated example would be to the right relativeto the upper/lower pieces 110, 130. Of course, because not all of theprobe pins are aligned at this point, free movement to the right (i.e.,as far as dowels 170 would allow) might not be possible initially.Thereafter, the path of the middle piece 120 is moved in a circularfashion with respect to the upper/lower pieces 110, 130. As best shownin FIG. 13B, which shows a single hole 120 a in the middle piece 120,this path 190 tends to catch the probe pins 150 at some point alongtheir cross section, and eventually coaxes the probe pins into theproper rotational alignment.

It is preferred to rotate the path 190 through at least one full circleand back to the eventual locking position, although more than one fullcircle could be transgressed to ensure that all of the probe pins havebeen coaxed and are rotating within their probe pin holes (“a”).Movement of the middle piece 120 can be performed by hand, althoughmovement of the middle piece 120 can also be automated as discussedearlier. Regardless of the method used to move the middle piece 120,care should be taken not to force the middle piece 120 to follow astrict set path 190, as this could damage probe pins that are not yetproperly rotationally aligned. Experience teaches that an operatormoving the piece 120 by hand can tell when the middle piece 120 isbinding and should not be forced further. When using automated alignmentprocesses, feedback should be gauged and limits set to ensure that themiddle piece 120 is not over-forced, and/or the path should beappropriately modified to ensure that alignment will be achieved. Onepossible alternative path 190 that might be suitable for such anautomated system is a spiral, in which the displacement of the middlepiece 120 from the upper/lower pieces 110, 130 is gradually radiallyincreased as the middle piece is rotated around.

In any event, the end of the probe pin alignment procedure discussedabove preferably results in bringing the middle piece 120 to a positionwhich locks the aligned pins. As noted earlier, in the illustratedexample, this occurs by moving the middle piece 120 to the right, asshown in FIG. 14. With the pins aligned, it can be seen that the middlepiece 120 comes to rest within a bend in the probe pin 150. Because themiddle piece 120 is bounded by this bend, the probe pin 150 will berestrained in its vertical movement, and thus becomes captured in thestack of the Z-block 100. With the pins aligned and locked into place,the assembly can be finally locked. Such locking is illustrated in FIG.15, in which a third set of dowels 200 are press-fit into the “d” holesin the assembly. In this regard, note that the “d” holes in the middlepiece 120 have been offset relative to the probe pins holes (“a”) suchthat bringing the piece 120 into the locked position renders the “d”holes wide open (see FIG. 14) and ready to receive dowels 200. Thisthird set of dowels 200 are similar in construction to the first set ofdowels (170), and are press fit into the slightly smaller diameter “d”holes, which like the “b” holes are approximately 0.97 mm in diameter.

At this point, the Z-block 100 assembly is finished, and advantages ofthe disclosed method can be appreciated. First, it is easy to mount theprobe pins into the Z-block, as the holes into which the probe pins areput are straight cylindrical holes (see FIG. 12). There is no need tosandwich the probe pins between two pieces of the Z-block, which asnoted earlier has the propensity to damage them. The probe pins can allbe aligned to a common orientation. Moreover, pins of varying geometriescan be used when compared to the prior art methods disclosed earlier;for example, the pins of FIG. 3 can be captured and used with thedisclosed Z-block approach even though they have larger effectivediameter probe ends (FIG. 3, 32 a). Additionally, the Z-block isrelatively easy to service. If necessary, the pieces can be gently priedapart—for example, using a razor blade—to loosen the dowels 170, 200present in the final assembly. After the dowels are loose, andspecifically dowel 200, the middle piece 120 can be moved to unlock theprobe pins 150 for easy retrieval.

It should be noted that to lock the probe pins 150 in place, it is notnecessary for the middle piece 120 to contact the pin in the horizontaldirection, as is shown in FIG. 15. Instead, it is sufficient that thepin movement be impeded in the vertical direction so that the pins won'tslip out of the probe pin holes (“a”). Such a means of capturing theprobe pins is satisfactory even if the pins are allowed some verticalplay within the probe pin holes (“a”). However, in a given design, itmay be desired that the pins be more firmly held in the horizontaland/or vertical directions, and if so the middle piece can be made tocontact the horizontal or vertical surfaces of the probe pins 150 bychoosing appropriate hole spacing and piece thicknesses given the probepin design at issue.

The disclosed alignment method (see FIG. 13) may cause the probe pins tocome to rest at different heights after they are locked. Consider forexample helical probe pins. If one probe pin is rotated three-quartersof a turn during alignment, and another is only rotated half a turn,when locked they may come to rest at different heights given theirhelical nature. Should this cause concerns, the protruding probe tips inthe Z-block 100 can be planarized after their manufacture and capture,for example, by using Chemical-Mechanical Planarization (CMP)techniques.

Many useful modifications can be made to the disclosed Z-block design.For example, and as shown in FIGS. 16A-16D, several different types ofprobe pins designs can be used. The illustration of these different pintypes shows that the design of the pin can dictate a logical design forthe Z-block, and in particular the design of the thicknesses used forthe various pieces so that the middle pieces will most logically line upwith and capture the probe pin at issue. For example, in FIG. 16B, themiddle piece 120 is thicker to accommodate a thicker recess in the probepin used in that Z-block. In FIG. 16C, the probe pin holes (“a”) in themiddle piece have beveled edges designed to mate with the spring (orhelix) used for the probe pin. FIG. 16D shows a simplified design for a“pogo pin,” which has a spring inside of a cartridge. As seen, thecartridge has a niche cut out of it to mate with the middle piece 120during locking.

Moreover, different locking schemes can be used that don't requirelinear shifting of the middle piece 120 to lock the pins. For example,as shown in FIG. 17, the “d” locking holes in the middle piece 120—i.e.,those used to finally lock the probe pins into position—can be offsetset at an angle relative to the corresponding locking holes (110 d, 130d) in the upper/lower pieces 110, 130. Accordingly, to lock the probepins, the middle piece 120 would simply be rotated with respect to theupper/lower pieces 110, 130.

While the use of three pieces is particularly useful, other number ofpieces could also be used, as illustrated in FIGS. 18A-18C whichillustrates the use of Z-blocks with two pieces (FIG. 18A), four pieces(FIG. 18B), or five pieces (FIG. 18C) in which some or all of the piecesstand in slidable relation to one another. FIG. 18A is particularlyinteresting as it contains countersunk probe pin holes in the lowerpiece 130 to allow a portion of the probe pin to pass through to theupper piece 110 and ultimately out of the Z-block. By moving the upperpiece 110 relative to the lower piece 130 (much as the middle piece 120was moved in earlier embodiments), the probe pins can be aligned andlocked.

While disclosed in the context of testing wafers, it should beunderstood that the disclosed Z-block can be used to test other sorts ofplanar electrical structures, such as PCBs. Moreover, while disclosed asbeing beneficial to the testing of entire wafers, the disclosed Z-blockcan be used to test individual chips on a wafer as well, and as such canbe used in a more traditional wafer probe fashion.

Although it is preferred that the various pieces touch one another toform a stack of pieces, this is not strictly necessary, as the piecescan have spaces between them, which may ease their slidability.Referring to “stacked” pieces should thus be so understood.

Thus, it should be understood that the inventive concepts disclosedherein are capable of many modifications. To the extent suchmodifications fall within the scope of the appended claims and theirequivalents, they are intended to be covered by this patent.

1. A contact system for interfacing an electrical circuit to anelectrical tester, comprising: at least two stacked pieces, wherein eachof the pieces comprises: a plurality of probe pin holes that formvertical sets of corresponding probe pin holes in the stacked pieces,each set of probe pin holes comprising a probe pin for making electricalcontact to the electrical circuit and the electrical tester; a pluralityof first locking holes that form vertical sets of corresponding firstlocking holes in the stacked pieces, wherein alignment of thecorresponding first locking holes in each set causes alignment of thecorresponding probe pin holes to allow for insertion of a probe pinthrough each set of corresponding probe pins holes; and a plurality ofsecond locking holes that form vertical sets of corresponding secondlocking holes in the stacked pieces, wherein alignment of thecorresponding second locking holes in each set causes misalignment ofthe corresponding probe pins holes to capture the inserted probe pins ina captured position.
 2. The contact system of claim 1, wherein thecaptured probe pins are rotationally aligned in each set ofcorresponding probe pins holes.
 3. The contact system of claim 1,wherein the at least two stacked pieces are slidable with respect toeach other to align or misalign the corresponding probe pin holes ineach set.
 4. The contact system of claim 1, wherein the pieces areinsulating.
 5. The contact system of claim 1, wherein the probe pins arenot rotationally symmetric about their long axes.
 6. The contact systemof claim 1, wherein the first locking holes are the same size in each ofthe pieces, and wherein the second locking holes are the same size ineach of the pieces.
 7. The contact system of claim 1, wherein the setsof first locking holes comprise first locking pins when the sets offirst locking holes are aligned, and wherein the first locking pins aredifferent from the probe pins.
 8. The contact system of claim 7, whereinthe sets of second locking holes comprise second locking pins when thesets of second locking holes are aligned, and wherein the second lockingpins are different from the probe pins.
 9. The contact system of claim1, wherein each of the pieces further comprises: a plurality of thirdlocking holes that form vertical sets of corresponding third lockingholes in the stacked pieces.
 10. The contact system of claim 9, whereinthe third locking holes are different sizes in the two pieces.
 11. Acontact system for interfacing an electrical circuit to an electricaltester, comprising: an upper piece, a middle piece, and a lower pieceformed in a stack, wherein each of the pieces comprises: a plurality ofprobe pin holes that form vertical sets of corresponding probe pin holesin the stacked pieces, each set of probe pin holes comprising a probepin for making electrical contact to the electrical circuit and theelectrical tester; a plurality of first locking holes that form verticalsets of corresponding first locking holes in the stacked pieces, whereinalignment of the first locking holes in the middle piece withcorresponding first locking holes in the upper and lower pieces causesalignment of the corresponding probe pin holes to allow for insertion ofa probe pin through each set of corresponding probe pins holes; and aplurality of second locking holes that form vertical sets ofcorresponding second locking holes in the stacked pieces, whereinmisalignment of the second locking holes in the middle piece withcorresponding second locking holes in the upper and lower pieces causesmisalignment of the corresponding probe pins holes to capture theinserted probe pins in a captured position.
 12. The contact system ofclaim 11, wherein the captured probe pins are rotationally aligned ineach set of corresponding probe pins holes.
 13. The contact system ofclaim 11, wherein the middle piece is slidable with respect to the upperand lower pieces to align or misalign the corresponding probe pin holesin each set.
 14. The contact system of claim 11, wherein the pieces areinsulating.
 15. The contact system of claim 11, wherein the probe pinsare not rotationally symmetric about their long axes.
 16. The contactsystem of claim 11, wherein the first locking holes are the same size ineach of the pieces, and wherein the second locking holes are the samesize in each of the pieces.
 17. The contact system of claim 11, whereinthe sets of first locking holes comprise first locking pins when thesets of first locking holes are aligned, and wherein the first lockingpins are different from the probe pins.
 18. The contact system of claim17, wherein the sets of second locking holes comprise second lockingpins when the sets of second locking holes are aligned, and wherein thesecond locking pins are different from the probe pins.
 19. The contactsystem of claim 11, wherein each of the pieces further comprises: aplurality of third locking holes that form vertical sets ofcorresponding third locking holes in the stacked pieces.
 20. The contactsystem of claim 19, wherein the third locking holes are the same size inthe upper and lower pieces, but a different size in the middle piece.21. A method for making a contact system for interfacing an electricalcircuit to an electrical tester, wherein the contact system comprises atleast two stacked pieces, wherein each of the pieces comprises probe pinholes that form vertical sets of corresponding probe pin holes in thestacked pieces, the method comprising: aligning corresponding probe pinholes in each probe pin hole set by aligning a plurality of firstvertical sets of corresponding first locking holes in the pieces;inserting probe pins within each aligned set of corresponding probe pinholes; and moving at least one of the pieces to align a plurality ofsecond vertical sets of corresponding second locking holes in thepieces, thereby misaligning the corresponding probe pin holes in eachprobe pin hole set to capture the inserted probe pins.
 22. The contactsystem of claim 21, wherein capturing the probe pins rotationally alignsthe probe pins.
 23. The contact system of claim 21, wherein the piecesare insulating.
 24. The contact system of claim 21, wherein the probepins are not rotationally symmetric about their long axes.
 25. Thecontact system of claim 21, wherein the first locking holes are the samesize in each of the pieces, and wherein the second locking holes are thesame size in each of the pieces.
 26. The contact system of claim 21,wherein aligning the corresponding probe pin holes in each probe pinhole set comprises placing first locking pins in the aligned pluralityof first vertical sets of corresponding first locking holes, wherein thefirst locking pins are different from the probe pins.
 27. The contactsystem of claim 26, wherein misaligning the corresponding probe pinholes in each probe pin hole set comprises placing second locking pinsin the aligned plurality of second vertical sets of corresponding secondlocking holes, wherein the second locking pins are different from theprobe pins.
 28. A method for making a contact system for interfacing anelectrical circuit to an electrical tester, wherein the contact systemcomprises an upper piece, a middle piece, and a lower piece formed in astack, wherein each of the pieces comprises probe pin holes that formvertical sets of corresponding probe pin holes in the stacked pieces,the method comprising: aligning corresponding probe pin holes in eachprobe pin hole set by aligning a plurality of first vertical sets ofcorresponding first locking holes in the pieces; inserting probe pinswithin each aligned set of corresponding probe pins holes; and movingthe middle piece with respect to the upper and lower pieces to align aplurality of second vertical sets of corresponding second locking holesin the pieces, thereby misaligning the corresponding probe pin holes ineach probe pin hole set to capture the inserted probe pins.
 29. Thecontact system of claim 28, wherein capturing the probe pinsrotationally aligns the probe pins.
 30. The contact system of claim 28,wherein the pieces are insulating.
 31. The contact system of claim 28,wherein the probe pins are not rotationally symmetric about their longaxes.
 32. The contact system of claim 28, wherein the first lockingholes are the same size in each of the pieces, and wherein the secondlocking holes are the same size in each of the pieces.
 33. The contactsystem of claim 28, wherein aligning the corresponding probe pin holesin each probe pin hole set comprises placing first locking pins in thealigned plurality of first vertical sets of corresponding first lockingholes, wherein the first locking pins are different from the probe pins.34. The contact system of claim 33, wherein misaligning thecorresponding probe pin holes in each probe pin hole set comprisesplacing second locking pins in the aligned plurality of second verticalsets of corresponding second locking holes wherein the second lockingpins are different from the probe pins.